These experiments combine immunological and electrophysiological techniques to investigate the regulation of neuroendocrine activity in the central nervous system of the marine mollusc Aplysia. The neuroendocrine bag cells synthesize a family of peptides which, when released, initiate a series of stereotypic behaviors leading to egg deposition. Although the bag cell system has been studied intensively for years, and has contributed substantially to the way we think about fundamental neuroendocrine processes, a crucial question has never been answered: what is the physiological stimulus that activates the normally quiescent bag cells? This proposal addresses that question. We take advantage of recent observations that the atrial gland, an exocrine organ in the reproductive tract, contains at least three peptides that can activate the bag cells. The receptive sites for these peptides will be mapped electrophysiologically by selective lesioning and application of peptides to specific regions of the central nervous system while recording from the bag cells and identified central nerrons. We will also develop monoclonal antibodies agains these structurally related peptides and use them to localize neuronal sources of peptides that could regulate bag cell activity. Finally, we will use electrophysiological techniques to characterize the functional connection between the cells that synthesize (and release) the regulatory peptides and the cells that respond to them.